The invention relates to a method for determining the mass of a motor vehicle while taking into account different driving situations. The method involves the evaluation of the respective vehicle acceleration, whereby in addition to the driving force of a vehicle drive unit the respective resistance forces resulting from rotational forces, from the air resistance, from the rolling resistance and from the slope descending force are taken into account. In addition to DE 197 24 092 A1 please refer in particular to DE 197 28 867 A1 for the technical scope.
For instance, for more complex chassis control systems under development it is desired or even necessary to have knowledge available regarding the current mass or the current weight of a motor vehicle, also of a passenger motor vehicle. Naturally the total weight of a specific vehicle depending on the load condition and on the fill level in particular of the fuel tank can vary over a relatively wide range. At first view, the easiest solution for determining the vehicle weight is using a suitable load-sensing device attached in the wheel suspension, however this is not practical for series production for cost reasons among other things. The same is true for pressure measurement in a vehicle's pneumatic suspension system if the vehicle is equipped with a pneumatic suspension system at all.
For example from the above mentioned documents another approach is known, however up to now it has been tested only with commercial vehicles such as heavy goods vehicles or the like. With the second mentioned DE 197 28 867 A1 a mass value representing the vehicle mass of a commercial vehicle equipped with a drive unit is determined by recording at least a first as well as a second acceleration value of the vehicle. These acceleration values represent the vehicle acceleration at a first and a second point in time at which the drive values representing the driving force or the driving torque are recorded. At least depending on the recorded acceleration values and the recorded drive values then at least a first and a second driving resistance value will be identified. Thereby the vehicle mass value is determined as a function of a comparison of at least the first identified vehicle resistance or estimated mass value with the second identified vehicle or estimated mass value. This comparison enables the recognition of a roadway gradient through which an incorrect mass identification caused by the roadway gradient is supposed to be prevented.
According to the first DE 197 24 092 A1 mentioned above the vehicle mass of a commercial vehicle with a towing vehicle and a trailer or semi-trailer, comprising an activatable braking device that acts upon the wheels of the towing vehicle and trailer/semi-trailer, is also determined through the vehicle acceleration. An initial acceleration value is recorded that represents the vehicle acceleration before activation of the brake device, as is at least a second acceleration value that represents the vehicle acceleration after activation of the brake device. The vehicle mass or a signal representing the vehicle mass is then determined or generated as a function of the first and second recorded acceleration values.
Based on the fact that these familiar mass determination methods or mass estimation methods have only been tested for relatively heavy commercial vehicles, it can be concluded that these methods are relatively inaccurate, i.e. that a relative large dispersion of the measurement results occurs. However this can be tolerated with large commercial vehicles whose empty weight and load weight significantly differ from one another. Significantly more accurate results should be provided by such a method for passenger vehicles since otherwise such a calculation practically would not need to be conducted, but rather an approximation value could be simply used that would be formed from the empty weight as well as an average payload.
Therefore it is the object of the present invention to further expand a method for determining the mass of a motor vehicle while taking different driving situations into consideration, involving an evaluation of a vehicle acceleration, wherein apart from a driving force of a vehicle drive unit, resistance forces resulting from rotational forces, air resistance, rolling resistance, the slope descending force and a braking force are taken into consideration, to the effect that a sufficiently accurate mass estimation can be made possible based virtually on the information that is already available in the vehicle or can be obtained through a suitable sensor or signal evaluation.
The solution to this object is characterized in that in the same approach the respective braking force is also taken into account. Particularly good results will be obtained thereby when a multitude of different driving situations is evaluated, whereby the individual results are each stored and combined to form a collective mass value. Thereby the proposed method can be further improved when the individual results are weighted differently. Additional embodiments are discussed herein.